Method of controlling oil refining processes



METHOD CONTROLLING OIL REFINING PROCESSES Robert E. Farrell, Maple Heights, and Janet E. Pack, ,Cleveland, Ohio, assignors to The Standard Oil' Company, Cleveland, Ohio, a corporation of' Ohio Na Drawing. Filed Nov. 21, 1957, set. N0. sensor 2 Claims. or. 208139) The present invention relates to a method of con= trollinga petroleum refining process. More particularly, the invention relates to the control of a petroleum refining process wherein the hydrocarbons undergo a change in phemical structure, e.g., the catalytic reforming of naphthas derived from crude petroleum. j I

Catalytic reforming is a process which has been widely. utilized in the petroleum refining industry in the past few years with the advent of the high octane require ments of fuels employed in modern high-compression ratio, internal combustion engines. Various processes for carrying out the catalytic reforming operatiQns have been developed and these are well known to those skilled intheart. One such process is the platforming process. The latter process involves the treatment ofnaphtha under. conditions of elevated temperature and pressure in the presence of hydrogen and a catalyst. The catalyst employed in this process isa composite of platinum, alumina, and combined halogen. The octane numberof a straight run or coker naphtha may be greatly enhanced by means ofthis process and products having octane numbers of 95 or above may be obtained from this process.

. .One of the characteristics of a catalytic reforming process is that the severity of the conditions employed in the. reaction will determine the final quality ofjthe product as well as the yield. Since octane number isthe chief criterion employed in the evaluation of fuel quality from the standpoint of engine performance, it isthe octane number that is usually employed as a quality standard inthe operation of the process.

However, as the octane number of the naphtha is itnpro'vcd theyield of liquid products from the reaction Suitable for use in motor fuel gradually declines; This effect on yield becomes greater if the octane number of the product approaches the upper theoretical limit. In one experiment which was conducted on a Pennsylvania straight-run naphtha, it was determined that in increasing the octane number of the product from 85.2 to 88.3 (F-l clear) the total'yield of C gasoline dropped from 80.4

1078.4 volume percent. It is, therefore, quite apparent that from an economic standpoint a catalytic reforming operation must be carried outso that the desired octane number of the product is approached as closely as possible; If the conditions of operation are suchthat the octane number of the product is one number higher than that which: .is' desired, an economically important decrease in the yield of the 3 gasoline results. However, it is notpossible to obtain rapid analysis ofthe product employing conventional laboratory techniques for evaluating octane number. If the octane number measurement is to be of any value in the operation of the process, it should be available to the operators of the plant within a short time after the sample is taken. Since it is not possible to do this by conventional octane rating techniques, various alternative methods of product analysis have been examined. One such analytical 2 scheme which had been proposed by the prior art involved the use of a continuous refractometer (Industrial & Engineering Chemistry, vol. 45, 1953, page 2381). While this method would provide some useful information, it was found that it was notalways entirely reliable since products havingsignific'antly different actual octane numbers would Ofll'ljhdVe about the same refractive index. In other words, it was not possible in all cases to reliably relate octane number to the refractive. index.

We have discovered that the disadvantages of this method can be overcome by the introduction of another parameter into the analytical technique, i.e., that if a colorimetric measurement is made on the product together with the refractive index measurement, a reliable mathematical co-relation can be obtained which will cor-' respond to the octane number of the product as determined by the conventional techniques. According tothe process of this invention, therefore, the product of a catalytic reforming operation is subjected to colorimetric as well as refractive index analyses and the conditions of the catalytic reforming process are altered or varied in accordance with these measurements.

The method of this invention may be carried out either continuously or intermittently depending upon the needs of the particular process. It is, of course, necessary to employ {mathematical analysis in order to corelate the color data with the refractive index data so as to obtain a reasonable co-relation with the octane number. 'Howeve'r, the mathematical techniques by which the necessary co-rclation is obtained are well known to those skilled in the art and a simple multiple regression analysis on any given set of data will usually provide the necessary .co-relation.

Refractive index (n 9 is a Well-known physical characteristic of liquids, and well-known instruments and measurement techniques are available and any of these may be used. Any conventional refractometer may be employed in connection with this process and it may be continuous or not. The preferred form of refractometer operates by comparingthe refractive index of a liquid standard with a liquid sample obtained directly from the process line and operates in the following manner: Light from an incandescent lamp collimated by a slit-and-lens system traverses two adjacent liquid prism cells where the beam is bent in proportion to the refractive index. The beam emerging from the" cells is focused by a lens and then redirected toward two photocells by a refractor block mounted on a turntable which is positioned by a servo-motor. The beam is split into two parts by a light barrier just before reaching the photocells. At balance, the image of the slit is evenly divided so that each photocell receives an equal ainount of light. When the refractive index of the liquid sample in the prism cell changes, a greater amount of light will fall on one of the photocells. Since the photocells are electrically connected in opposition, the amplifier difference signal will drive the refractor-block positioning motor until light falls equally on both photocells, thus restoring balance.

One of the hollow prism cells mentioned heretofore will contain a standard liquid sample while the other cells contain the sample which is to be measured. When both samples have the same index of refraction, there is no. deviation ofthe light beam as it passesthrough the two liquids. Composition changes in the flowing sample deflect the beam in proportion to the refractive index difference of the sample and standard. Deviation of the beam causes one photocell to receive more light than the other. The resulting signal to the amplifier starts the motor, which turns the refractor block toward a balanced condition. The displacement of the refractor block required to achieve balance is proportional to the differ- Patented Feb. 21, i:

ence in refractive index between sample and standard.

A Helipot is geared to the motor shaft to operate a potentiometric recorder.

As in the case of refractometer, a conventional colorimeter may be employed in connection with this process and it may be continuous or not. A continuous colorimeter is composed of a light source compartment, a flow chamber, and a receiver compartment. In operation, the instrument uses the same physical relationships to measure color intensity as those employed in the field of spectrophotometry. Light from any convenient source such as a tungsten lamp passes through a filter which selects the desired wave length, then it is directed through the process fluid in the flow chamber. The process fluid will absorb a certain amount of the light, depending upon its color intensity. The remaining light passes through the process stream, is detected by a sensitive phototube and it is then electrically amplified. The amplified signal drives a direct-reading meter and a standard potentiometric recorder. Good voltage regulation and stable feedback amplification will insure the accuracy of the instrument.

When the refractive index and color of a sample have been measured, the octane number of the sample is determined by the following formula:

Octane number (F1 clear)= -k +k (n +k (A) where I n is the refractive index at 20 C.

A is the color absorbance k k and k;, are constants determined by a regression analysis from a number of similar samples The following example is illustrative of the manner in which the process of this invention is carried out:

A catalytic reformer was operated at a feed rate of 12,000 bbl./day employing a feed material boiling in the range of 200 to 400 F. This feed contained 85% virgin naphtha derived from an East Texas crude and 15% of a coker heavy distillate. The feed had been pretreated to remove sulfur and ammonia and other catalyst poisons. The conditions of the reforming operation were as follows:

Reactor temperatures 970 F. Pressure 500 p.s.i.g. Catalyst (The usual platforming catalyst of the platinum alumina combined halogen type.) Ratio of hydrogen to hydrocarbon in feed to the reactors 8 to 1.

It was desired to conduct this reforming operation to reach a target level octane of 85 (F-l clear) for the reformate. After the unit had been in operation a sufficient length of time to stabilize conditions, a sample of the reformate was withdrawn. A refractive index measurement was made in a refractometer on this product and it was detemrined that the product had a refractive index of 1.43175. The same product was then analyzed in a colorimeter having a cm. cell at a wave length of 425 mu which is the preferred wave length for the analysis of a reformate. The color absorbance of the reformate was determined to be 148.0. Based on previous analysis of a number of similar products and a mathematical analysis of the data obtained thereby, a mathematical formula for the octane number was developed and it is:

Octane number (F-l clear)==-443 Inserting the actual values measured in this experiment, the octane number was determined to be 87.5. A portion of the same sample was then'analyzed in the conventional manner in a laboratory motor, and the F-1 octane number by the conventional laboratory method was determined to be 87.4 which is in good agreement with the new method of determining the octane number. Thus, it was apparent that the target octane number had been exceeded and the reactor temperature at the reformer was lowered to 960 F. to give the desired product octane number.

The significance of this measurement is illustrated by the fact that a mathematical correlation based on the refractive index alone would have indicated that the oc ane number of the product was 83.1. Such an inaccurate measurement would have induced the operators to raise the reactor temperatures in order to increase the obtane number of the product. This, of course, would have tended only to further increase the octane number and would have resulted in an uneconomic yield loss in the unit. Thus, it is believed apparent that the method of this invention provides a new and beneficial method of control for catalytic reforming operations.

While the present invention has been described in relation to catalytic reforming operations, it is equally applicable to other petroleum refining processes. For example, a light naphtha catalytic isomerization unit could be controlled in the same manner. It is believed that the invention would also be applicable to catalytic cracking operations. Accordingly, this application for Letters Patent is not deemed to be limited except by the appended claims.

We claim: 1. A method of controlling a catalytic hydrocarbon conversion process which comprises the steps of obtaining a sample of the product of said process, measuring the refractive index at a predetermined temperature and also measuring the color of said sample, correlating said refractive index measurement with said color measurement whereby an indication of the quantity of the product is obtained, and altering the operating conditions of said refining process when said indication of product quality deviates from the desired product quality whereby the product quality will be altered to correspond to said desired product quality.

2. A method of controlling a catalytic naphtha reform.- ing process which comprises the steps of obtaining a sample of the product of said process, measuring the refractive index at a predetermined temperature and also measuring the color of said sample, correlating said refractive index measurement with said color measurement whereby an indication of the quality of the product is obtained. and altering the operating conditions of said reforming process when said indication of product quality deviates from the desired product quality whereby the product quality will be altered to correspond to said desired product quality.

References Cited in the file of this patent UNITED STATES PATENTS Latchum Nov. 7, 1950 Ebers Mar. 13, 1953 OTHER REFERENCES Diller et al: Industrial and Engineering Chemistry,

pages 367-373. volume 15, June l5, 1943.

Gas Oil and Fuel Analysis by Engelder" (page 136),

+ ("D A John Wiley and Sons 1931 

2. A METHOD OF CONTROLLING A CATALYTIC NAPHTHA REFORMING PROCESS WHICH COMPRISES THE STEPS OF OBTAINING A SAMPLE OF THE PRODUCT OF SAID PROCESS, MEASURING THE REFRACTIVE INDEX AT A PREDETERMINED TEMPERATURE AND ALSO MEASURING THE COLOR OF SAID SAMPLE, CORRELATING SAID REFRACTIVE INDEX MEASUREMENT WITH SAID COLOR MEASUREMENT WHEREBY AN INDICATION OF THE QUALITY OF THE PRODUCT IS OBTAINED, AND ALTERING THE OPERATING CONDITIONS OF SAID REFORMING PROCESS WHEN SAID INDICATION OF PRODUCT QUALITY DEVIATES FROM THE DESIRED PRODUCT QUALITY WHEREBY THE PRODUCT QUALITY WILL BE ALTERED TO CORRESPOND TO SAID DESIRED PRODUCT QUALITY. 